Hypoxia-inducible factor 1 (HIF-1) is expressed in nucleated mammalian cells in response to reduced O2 availability. HIF-1 is a basic helix-loop helix PAS transcription factor consisting of HIF-1alpha and HIF-1beta subunits HIF-1alpha expression is quantitatively regulated by cellular O2 concentration and determines the biological activity of HIF-1. The molecular mechanisms by which hypoxia is sensed and the signal is transduced leading to increased HIF-1alpha expression are not well understood. HIF-1 activates transcription of genes encoding proteins that can be classified into several groups: (i) those that increase O2 delivery to ells, such as erythropoietin and vascular endothelial growth factor (VEGF), which stimulate erythropoiesis and angiogenesis, respectively, and nitric oxide (NO) synthase-2 and heme oxygenase-1, which synthesize the vasoactive molecules NO and CO, respectively; (ii) those involved in metabolic adaptation to hypoxia such as glucose transporters and glycolytic enzymes; and (iii) other growth/survival factors, such as insulin-like growth factor 2. HIF-1 has been shown to play a critical role in the development of the circulatory system during embryogenesis and its subsequent physiological regulation in postnatal and adult life. The proposed studies are based upon the hypothesis that HIF-1 plays an important role in responses to hypoxia/ischemia by myocardial cells. For example, the role of HIF-1 in activating expression of VEGF and promoting angiogenesis in the myocardium is well established. In this project, we will focus on three questions: First, what are the mechanisms by which HIF-1 activity is induced in myocardial cells? Second, what is the effect of HIF-1 expression of myocardial viability under induced in myocardial cells? Second, what is the effect of HIF-1 expression on myocardial viability under ischemic conditions in the presence or absence of prior precondition? Third, what genes are induced by hypoxia that may contribute to the second window of preconditioning and which of these genes are regulated by HIF-1?